Optical signaling is as an alternative to electrical signaling for high-speed short-reach communication links. Vertical-cavity surface-emitting lasers (VCSELs) typically are the light source in short-reach high-speed optical links. The light produced by the VCSEL is coupled to an optical medium (e.g., fiber or waveguide) and sensed at the receiver by, for example, a photodiode (PD).
Aging and temperature dependence are two issues that affect a VCSEL's operation. As the device ages or as the temperature increases, the VCSEL's output degrades from that of its nominal condition, causing a link to generate more bit errors or even to fail in the extreme case. The VCSEL's threshold current ITH increases with temperature and aging, while the slope efficiency η decreases. Both of these changes result in the VCSEL producing less output power for a given bias and modulation current.